1. Field of the Invention
The invention relates in general to methods involving interfaces adapted for use in coarse wavelength division multiplexing (CWDM) fiberoptic communication networks. Such interfaces are used to adapt, adjust or convert optical signals transmitted between different network units. Dense wavelength division multiplexing (DWDM) typically uses wavelength separations of about 1.6 nm. CWDM, on the other hand, typically has a wavelength separation in the order of about 20 nm. CWDM has inter alia the advantage that the different components used in the system are less expensive. Furthermore, the power requirements are usually lower compared to DWDM and also the physical size of the used laser is normally smaller and it is not cooled in a CWDM system.
2. Technical Background
FIG. 1 shows an example of a part of a fiberoptic communication network according to the prior art. The figure shows a subscriber or client unit 12 connected to a larger fiberoptic network 14 via an interface 10 and a multiplexer/demultiplexer 11. In a typical case the subscriber may be a company which may also have its own fiberoptic network. The subscriber may, for example, obtain access to the larger fiberoptic network 14 by an agreement with another company, which can here be called the provider. The provider may have several clients which all are connected to the larger fiberoptic network 14. The larger fiberoptic network 14 may for example be the Internet. The connection between the subscriber unit 12 and the interface 10 is normally bi-directional, which in this document means that signals can be sent in two opposite directions, indicated by arrows in FIG. 1. The communication is normally implemented via two optical fibers 16, 18. Also the communication between the interface 10 and the multiplexer/demultiplexer 11 normally takes place over two optical fibers 20, 22. The interface 10 is used to adapt the signals from the client unit 12 to the multiplexer/demultiplexer 11 and vice versa. The interface 10 may, for example, carry out wavelength conversion, amplification, signal conditioning, data regeneration, noise reduction etc. The interface 10 normally includes means for converting optical signals from the client unit 12 to electrical signals and means for converting electrical signals to optical signals before they are transmitted to the multiplexer/demultiplexer 11. The interface 10 also normally includes means for converting optical signals from the multiplexer/demultiplexer 11 to electrical signals and means for converting electrical signals to optical signals before they are transmitted to the client unit 12. The conversion in the different directions may be carried out via transceivers, 24, 26 which form part of the interface 10. The transceivers 24, 26 can be formed as pluggable modules which can be plugged into a circuit board.
The client unit 12 may be located at a shorter or longer distance from the interface 10.
FIG. 2 shows in more detail an example of an interface 10 according to the prior art and thus a known manner of connecting a subscriber unit 12 to a fiberoptic communication network 14 via a fiberoptic interface 10, which is adapted to function as an interface in a coarse wavelength division multiplex (CWDM) system.
It should be noted that the interface, as the concept is used in this document, includes the attached transceiver modules 24, 26. The concept “interface device” does however refer to the interface without the transceiver modules 24, 26.
The interface device 30 comprises an electric circuit arrangement 32, a first receiving section 34 adapted to receive a first opto-electric transceiver module 24 and a second receiving section 36 adapted to receive a second opto-electric transceiver module 26. The first opto-electric transceiver module 24 includes a first receiver unit 38 for receiving optical signals from an optical conduction path 22, the first receiver unit 38 comprising a first opto-electrical converter 40 for converting the received optical signals to electrical signals, which are adapted to be conducted to said electric circuit arrangement 32. The first opto-electric transceiver module 24 also includes a first transmitter unit 42 for transmitting optical signals to an optical conduction path 20, the first transmitter unit 42 comprising a first electro-optical converter 44 for converting electrical signals, received from said electric circuit arrangement 32, to optical signals before they are transmitted from the transmitter unit 42.
The second opto-electric transceiver module 26 is similar to the first opto-electric transceiver module 24 and thus includes a second receiver unit 46 for receiving optical signals from an optical conduction path 18, the second receiver unit 46 comprising a second opto-electrical converter 48 for converting the received optical signals to electrical signals, which are adapted to be conducted to said electric circuit arrangement 32. The second opto-electric transceiver module 26 also includes a second transmitter unit 50 for transmitting optical signals to an optical conduction path 16, the second transmitter unit 50 comprising a second electro-optical converter 52 for converting electrical signals, received from said electric circuit arrangement 32, to optical signals before they are transmitted from the transmitter unit 50.
The first 34 and second 36 receiving sections can be designed such that said first 24 and second 26 opto-electric transceiver modules may be plugged into the respective receiving section 34, 36 and unplugged therefrom in a quick-connect manner.
The interface device 30, together with said attached first 24 and second 26 opto-electric transceiver modules, is arranged to adapt the signals from said subscriber unit 12 before transmitting the signals to said multiplexer/demultiplexer 11, and also to adapt signals from said multiplexer/demultiplexer 11 before they are transmitted to said subscriber unit 12.
As has been mentioned above, the interface device 30 is normally connected to the subscriber unit by attaching said first 24 and second 26 opto-electric transceiver modules to said receiving sections 34, 36, by connecting the multiplexer/demultiplexer 11 to the first opto-electric transceiver module 24 via optical fibers 20, 22 and by connecting the subscriber unit 12 via the optical fibers 16, 18 to the second opto-electric transceiver module 26.
An interface device 30 of the above kind may be tested in order to make sure that the interface device 30 functions accurately. This test may be done before the interface device 30 is sold or used in the fiberoptic communication network. The testing can be done by arranging opto-electric transceiver modules 24, 26 in said first 34 and second 36 receiving sections. Furthermore, optical fibers 16, 18, 20, 22 are connected to said opto-electric transceiver modules 24, 26. The optical fibers 16, 18, 20, 22 are also connected to a test equipment. By sending appropriate optical pulses and monitoring the response in the test equipment, the function of the interface device 30 may be checked.
An interface as described above can be quite expensive. In particular the transceivers that form part of the interface are often expensive